Mupirocin

Mupirocin is a topical antibiotic used for impetigo, small areas of infected skin lesions and nasal decolonisation of Staphylococcus aureus including MRSA. It is not used systemically because it is inactivated rapidly. Resistance develops with repeated or prolonged use.

Classification. Pseudomonic acid derivative (topical antibiotic).

Mechanism. Binds isoleucyl-tRNA synthetase and blocks protein synthesis; bacteriostatic at low concentrations and bactericidal at the high concentrations reached topically.

Spectrum. Staphylococcus aureus (including MRSA), Streptococcus pyogenes and other streptococci. Little activity against Gram-negative bacteria or anaerobes. High-level resistance (mupA) is described.

Pharmacokinetics. Minimal absorption through intact skin; absorbed drug is rapidly metabolised to inactive monic acid and excreted by the kidneys. Absorption rises through damaged skin.

Topical use only; maximum 10 days a course.

Adults and children.

• Impetigo and small infected skin lesions (secondarily infected dermatoses, cuts, insect bites): apply 2% ointment or cream thinly to the lesion three times daily for 5 to 10 days; review at 3 to 5 days.
• Nasal decolonisation of Staphylococcus aureus or MRSA: apply 2% nasal ointment (a matchstick-head amount) into each nostril twice daily for 5 days, with chlorhexidine body wash on days 1 to 5 in hospital programmes; repeat screening after the course.
• Age: ointment and cream from 2 months of age; nasal ointment usually from 12 years (younger under specialist advice).

Alternatives. Fusidic acid (topical), retapamulin, antiseptic washes, oral flucloxacillin or cephalexin for extensive impetigo.

Contraindications. Hypersensitivity to mupirocin or the base; do not use on large open wounds or burns if the base contains polyethylene glycol and kidney function is impaired.

Adverse effects. Local burning, stinging, itching, rash and contact dermatitis, nasal irritation and dryness. Serious (rare): hypersensitivity, overgrowth of non-susceptible organisms, Clostridioides difficile infection (very rare).

Interactions. None of clinical importance when applied topically. Do not mix with other topical preparations.

Common prescribing errors. Use beyond 10 days (resistance), use for extensive disease, long-term nasal use, and use on large areas of broken skin with polyethylene glycol-containing ointment.

Special groups. - Pregnancy: acceptable when needed. Breastfeeding: acceptable; avoid applying to the nipple before feeding. - Older adults: usual use. - Kidney impairment: avoid polyethylene glycol-containing ointment on large areas of broken skin; use the cream. - Liver impairment: no adjustment. - Region: available in East Africa in limited quantity; resistance concerns argue for restricted use.

Administration. Wash hands and apply a thin layer with a clean applicator; cover with a light dressing if wished. Keep away from the eyes. Nasal: apply into the front of the nostrils and press the sides of the nose together.

Baseline and monitoring. - Baseline: lesion extent, MRSA history, skin integrity. - During treatment: review at 3 to 5 days; if no improvement, send a swab and consider oral treatment.

Stop rules. Stop for skin sensitisation or worsening, or when the course is complete.

Referral and escalation. Refer for extensive impetigo, cellulitis, systemic features, recurrent infection and persistent MRSA carriage.